Polymers



Patented Aug. 25, 1953 POLYMERS Robert N. MacDonald, New Castle, Del., assignor to E. I. du Pont de Nemours and Company,

11, DeL, a corporation of Delaware No Drawing. Application July 29 1950 sci-m No. 176,777

2 Claims. (Cl. 200-775) This invention relates to new condensation polymers and particularly to new alpha-amino acid polyamides.

Synthetic polyamides from alpha-monoaminocopolyamides (MacDonald U. 8. Patents 2,572,844 Thus, high molecular weight alpha-amino acid copolymers (MacDonald U. S. Patents 2,572,844 and 2,534,283, of which the present application is a continuation-in-part) can be prepared by copolymerizing the N-carboanhydrides of alphaprimary-aminocarboxylic acids containing at least one hydrogen on the alpha-carbon. However, these alpha-amino acid copolyamides, although useful in certain film and fiber outlets, are not as completely useful as is desired, particularly in those uses wherein "breathable" films are desired, i, e., films exhibiting water vapor permeability yet ood water insensitivity. This combination of water vapor permeability and water insensitivity is highly desirable for such uses as raincoats, wrapping materials for foods, and the like but the combination of properties is in general not found in the hitherto known alphaamino acid homopolyamides and copolyamides. In general these are either highly water insensitive and water vapor impermeable or are water vapor permeable but relatively water sensitive. Examples of the latter type 01' polyamides include those containing high proportions of combined DL-alsnine and/or N-substituted, i. e., alphasecondary amino acid units. Probably the most outstanding of these is DL-alanine homopolyamide. This polyamide is described in greater detail in the copending application of Miegel, Serial No. 197,513, filed November 24, 1950.

This invention has as an object the preparation of new alpha-monoaminomonocarboxylic acid polyamides. A further object is the provision of alpha monoaminomonocarboxylic acid polyamides which in film or sheet form are water vapor permeable but at the same time water resistant. Another object is the provision of synthetic optically inactive alpha-amino acid polyamides having outstanding strength in film and fiber form. A still further object is the provision of a new intermediate for polyamides. jects will appear hereinafter.

These objects are accomplished by the invention of DL-methionine-N-carboanhydrides and of polyamides having in effective amount, preferably in predominant amount, and even more preferably, essentially exclusively, DL-methionine Other obrecurring units. Synthetic alpha-monoaminomonocarboxylic acid Do yamides containing a preponderance of combined DL methionine units-particularly the homopolyamide or DL- methionineare surprisingly among the strongest synthetic, optically inactive alpha-amino acid polyamides in film or fiber form thus far discovered. These DL-methionine polyamides, particularly the homopolyamide, like the DL-alanine polyamides, particularly the homopolyamide, in film form, as cast, exhibit an X-ray difiraction pattern which shows no apparent orientation in its outermost rings. These two families of alphaamino acid polyamides, i. e., the DL-alanine and DL methionine polyamides, particularly the homopolyamides, are diilerentiated from other known alpha-amino acid polyamides in their ability to produce surprisingly strong films and fibers, especially after the polyamide is oriented.

The DL-methionine polyamides, particularly the homopolyamide, are distinguished from the DL-alanine polyamides, particularly the homopolyamide, in being water vapor permeable but also highly water insensitive. Furthermore, these DL methionine polyamides, particularly the homopolyamide, possess extralinear groups, 1. e., extralinear methyl thioether groups, which are capable oi ready modification by chemical means. Such modifications, for example, conversion of the extralinear methyl thioether groups to alkyl sulionium salts, methyl sulioxy, or methyl sulfone groups, are particularly eillcacious in achieving many desired goals-for instance, modifying the organic solubilities oi the polyamides or making them controllably more responsive to aqueous processing treatment.

The polyamides of this invention have a chain which consists of recurring atom groups and can be conveniently prepared by polymerizing the amide-forming derivatives, e. g.. the esters, the N-carboanhydrldes, etc. of DL- methionine (racemic methionine) with or without the amide-forming derivatives oi other alpha-aminomonocarboxylic acids. Among the known amide-forming derivatives of the alphaamino acids, it is preferred to use the N-carboanhydrides since they can be conveniently prepared in good yields from readily available materials and are capable of being easily polymerized with evolution of carbon dioxide to high molecular weight filmand fiber-forming alphaamino acid poly-amides. The new compound Iii-methionine N-carboanhydride also constitutes a part or this invention.

As used in these examples, inherent viscosity, man, is defined by the iollowing iormula wherein In is the natural logarithm;

I solution I solvent Example I A suspension of 50 parts oi DL-methionine in 1070 parts 01' purified anhydrous dioxane in a reactor fitted with an efflcient stirrer, a reflux water condenser, and a gas inlet tube connected to a source oi gaseous phosgene and so placed that its lower extremity is just above the suriace oi the suspension is treated with gaseous phosgene ior 44 minutes while maintaining the temperature oi the reaction mixture between 40 and 51 C. at such a rate that an excess of phosgene is added. At the end oi this time, the dioxane is removed by distillation at 50 C. under the reduced pressure obtained from a water aspirator. The yellow syrup remaini I Ill.

ng is dissolved in 790 parts of anhydrous diethyl ether and the resulting solution filtered to remove the small portion oi DL-methionine hydrochloride obtained. To the filtrate is then added 455 parts oi petroleum ether (13. P. 30-60 C.) and the resulting mixture cooled in a solid carbon dioxide/acetone bath. The crystalline product (34 parts), which soon separates out, is removed by filtration. To the filtrate is added an additional 910 parts of petroleum ether and the resulting mixture cooled in an ice/water bath. There is thus obtained an additional 10 parts oi product. The combined 44 parts oi DL-methionine N-carboanhydride (75% oi theory) is twice recrystallized irom a diethyl ether/petroleum ether mixture using 15.9 parts oi diethyl ether and 3.8 parts oi petroleum ether for each part oi N-carboanhydride. A small amount oi decoloring charcoal is used during each recrystallization to remove traces oi colored impurities. The final, twice recrystallized DL-methionine N-carboanhydride is obtained as white needle crystals melting at 44-46 C. and evolving gas vigorously at approximately 100 C.

Analysis.-Calculatcd ior CoHeOaNSt C, 41.14%; H, 5.15%. Found: C, 41.34%; H, 5.22%.

Example II Five (5) parts of the N-carboanhydride oi DL-methionine prepared as described above irom the corresponding amino acid is dissolved in 220 parts of reagent grade benzene, and the resulting solution heated under atmospheric pressure at the reflux while under anhydrous conditions for five days. The viscous, clear solution thus obtained is poured in a thin film onto a glass plate and the benzene allowed to evaporate at room temperature. Aiter being removed from the casting surface with the aid oi water and dried at 65 C. for six hours, there is obtained a clear, strong, tough, self-supporting, colddrawable film of the homopolyamide irom DL- methionine exhibiting an man. of 1.46 and soluble in benzene, m-cresol and tetrachloroethane. Samples of this film, as cast, exhibit a tenacity oi 9,700 lb./sq. in. and an elongation oi 8% as measured on the Instron tensile tester. Additional samples oi this film exhibit a water vapor permeability oi 2400-2550 g. of water/100 sq. m./mil/hour and a water absorption of only 8 to 4% upon being exposed to 100% relative humidity for 24 hours after being conditioned at relative humidity. Additional samples of this film aiter being drawn about 2.25:1 exhibit a tenacity oi about 18,000 lbJsq. in. and an elongation oi 12%. These results are the highest hitherto obtained for any synthetic, optically inactive alpha-amino acid polyamide.

A similar polymerization carried out under like conditions except that the solution was maintained at C. for seven days led to the production oi a DL-methionine homopolyamide oi 1mm. 0.74. A similar polymerization carried out for five days at 65 C. led to the production oi a DL-methionine homopolyamide oi 'ninh. oi 0.64.

The combination of relatively high water vapor permeability and relatively low water absorption is a unique property of the DL-methionine polyamides oi this invention. Other polymers known in the art are either highly water vapor impermeable and water insensitive, i.. e., nonabsorptive, or highl water vapor permeable and water sensitive. Thus, polyethylene, vinyl chloride/vinylidene chloride copolymers and rubber hydrochloride exhibit water vapor permeabilities of about respectively, 23-80, 11, and 40-60 grams of water/ sq. m./mil/hour and water absorptions of essentially 0% at 100% relative humidity. Similarly, a 35.5/26.5/38.0 hexamethyleneadipamide hexamethylenesebacamide/ epsilon-aminocaproic acid copolyamide exhibits a water vapor permeability oi 1250 and a water absorption oi 10.5% in the same units determined ln the same manner as described previously. Finally, untreated, i. e., non-moistureprooi, cellophane, a truly highly water vapor permeable polymer, exhibits a water vapor permeability oi 8000, but at the same time a water absorption oi 100%, both in the same units as described previously. Thus, the water vapor permeability oi 2500-2800 with a water absorption of only 3 to 4% for poly-DL-methionine is indeed surprising.

Ezrdmple III A mixture of iour parts oi DL-methionine homopolyamide and 214 parts oi methyl iodide are warmed at the reflux on a steam bath ior one hour. The polymer is removed from the resulting suspension and freed of excess methyl iodide by evaporation at room temperature. The product thus obtained (7.8 parts of the methylsuli'onium iodide of DL-methionine homopolyamide) is completely water-soluble. Aiter dissolving in about parts of formic acid, the resulting solution is poured onto a glass plate and the iormic acid allowed to evaporate at room temperature. Upon removal from the casting suriace, there is obtained a light brown-colored, seli-supporting film oi the methylsulionium iodide oi DL-methionine homopolyamide.

Example IV A solution of one part each oi the N-carboanhydrides oi DL-methionine and DL-alanine in. about 88 parts of reagent grade benzene is heated at atmospheric pressure under anhydrous conditions and at 65 C. for live days. During this 6'. timethe immthopolympartiuuui initsdesreeos merimtionmedilmasawhite tillaterial. mes to'aqueom processing by 'l'hisc poiyamideiromauibyweightmixnn-r ottheN-car withtheekbalinearmethylthioethermups. as ml-alanineissolubleinm-cresolandicrmieaeid. the orbit.- units uhibitinganm.oi0.22inthetormer.butis inthepolyamidesoithisinvention insolubleindioxaneandchloroi'onn. thereisa deseribedcapabilityoibeingecntrollabiymodi- 7 iled in m This becomes AsolutionoioneparteaehoitheN-carboan- 1o noticeable when the P lymers contain a major hydrides oi Bil-methionine and Dbleueine in proportion.i.e.morethan5o$ amt-methionine abeutsspertsorreagentgradebenseneisheated units- .whenthislatterlevei oi under atmoephericpressure andanhydrom eoncombined Dbmethionlne units is reached. the ditionsatdiiQiorflvedays. Attheendoithis mlylmidesoithisinvention v iwlarly time, the clear. viscous. but flowable. standing in exhibiting appreciable water vapor bensenesolutionoithoisflowedin v neab litvanda tbe ame mea sh s e aillm onto a class plate and thebensene solvent 01 i mit vityallowed to evaporate at room temperature. Upon removaliromthecastingsuriaeathereisthus extremely tough. cold-drawable fllmoithecopolyamideiromaiu byweight mixture of the N-carboanhydrides oi Dir-methionine and DL-leucine exhibiting ninn. of 1.04. This eopolyamide is soluble in chloroform. dioxane, and m-cresol.

Although in Example I certain conditions of reaction such as time. temperature, proportions. etc. have been given for the preparation oi the novel N-carboanhydride or this invention. it is to be understood that other methods known in the art for preparing N-carboanhydrides can also be used. For instance. the N-carboanhydride 0! this inventioncanbepreparedasisdisclosedinthe copending application oi Prichard, Serial No. 7'18,- 457. died October 7, 1947 (now U. 8. 2,516,146). by treating the requisite alpha-amino acid in an anhydrous solvent with an alkali metal alkoxide and with carbon dioxide thereby forming the dialkali metal salt oi' the alpha-carbonaminoearboxylic acid. reacting thionyl chloride with this salt, and finally isolating the desired N-carboanhydride.

The N-carboanhydride of this invention can alsobepreparedaslsdisclosedintheco application of MacDonald. Serial No. 83.299, filed March 24, 1949, by reacting the amino acid or its alkali metal or alkaline earth metal salts with phosgene under anhydrous conditions.

The novel N-carboanhydride of this invention also can be prepared by reacting the amino acid or its alkali metal. alkaline earth metal or hydrohalide salts with phosgene under anhydrous conditions in the presence of an ether. as is illustrated by Example I.

The novel N-carboanhydride of this invention can also be prepared, though with some dimeulty. item the corresponding amino acid as reported by Leuchs. Ber. 39. 857 (1906) by reacting the amino acid with a chloroiormate ester. ester or the N-carboxyamino acid so formed and subsequently reacting this derivative with thionyl chloride under anhydrous conditions and isolating the desired N-carboanhydride. Dii'ilculty is usually encountered in purifying DL-methionine N-carboanhydride so prepared to the degree of purity desired for polymerization.

This invention is also-generic to the polymers from the above N-carboanhydride. These polymers are linear condensation polyamides consisting of recurring alpha-monoaminomonocarboxylic acid units 10 to 100% of which are DL- methionine units. when at least 10% of the recurring units of the polyamides of this invention are composed 01' these residues. the poiyamide is capable oi controllable modiiication in its general lnthecaseoicopobmcm 1M bined residues. -NRCRR"CO. oi other alim Hll 1| M, $11M e a course. additional units in mmonocarboxylic acid hydroehl at least 10% oi chloride.

monocarboxylic acids. e

g., phenylalanine, alpha-phenylglycine, phenylalanine, and beta (in-tolyl) alanine; eycloaliphatic-substituted-aliphatic alpha-monoaminomonocarboxylic acids. e. g.. alpha-aminocyclohexylacetic acid; N aryl substituted alphasecondary-m onoearboxylic acids, e. g.. N-phenylglycine, N-o-tolylglycine; N-alkyl-substituted alpha secondary monoaminomonocarboxylic acids, e. g., N-methylglycine, N-isopropylglycine, N-butylglycine. N-octadecylglycine, N-isopropyileucin N-methylaianine.

The polyamides and copolyamides of this invention are preferably prepared in the p oi organic liquids by the condensation polymeriaation (thermal or initiated by water. alcohols. phenols, organic acids. or amino-hydrogen containing amines) or the previously defined monoaminomonocarboxylic acid N-carboanhydrides with carbon dioxide evolution. The N- carboanhydrides are preferably made from the amino acids or their inorganic acid. alkali metal. or alkaline earth metal salts, by reaction with phosgene as detailed above. Suitableorganic liquids that can be used tor the polymerization properties, as affected assess 7 include aromatic hydrocarbon e. g.. benaenc. xylene; halogenated hydrocarbons. e. 3.. chloroform. chlor. tetrachlorwthane. carbon tetrachloride; alicyclic ketones. e. g.. cyclohexanone; hydrocarbon ethers. e. g.. anisoie and diare suitably heated in escaping carbon temperature at which carbon dioxide begins to be evolved at an appreciable rate under the conditions of reaction. This varies amino acids. but it is usually in to 200 C. and generally within 30-50" C. of the melting point of the lowest melting N-carboanhydride present in the mixture to be olymerized. The time of the reaction can be shortened or the temperature can be lowered or both can be accomplished by the use oi reaction initiators. e. g., water. alcohols. phenols. organic acids or amino hydrogen-containin amines.

The polyamides or this invention containing appreciable proportions oi. combined DL-methionine units. as has been discussed previously. are characterized by the ease or controllable modification in properties, particularly in solubility through structural modification or the polyamides by chemical reactions carried out on the extralinear methyl thioether groups. As the proportions of combined DL- methionine units increase the properties of the polyamides become more nearly those of DL- methionine homopoiyamide. For instance. when a preponderance, alpha-amino acid units in the polyamides oi this invention are DL-methionine units. the polyamides are surprisingly strongparticuiarly when oriented, water insensitive and at the same time appreciably water vapor permeable. As the proportion of combined Dis-methionine units oi the polyamides 01' this invention increases still further, for instance, 75% or more or the alphaamino acid units, these polyamides are appreciably stronger. particularly when oriented, and appreciably more soluble in aromatic hydrocarbon and halogenated hydrocarbon type solvents than most or the other alpha-amino acid polyamides. This is particularly true when the polyamides of this invention are contrasted with i. e., more than 50%, oi the 8 containinc major proportions of units or straisht-chain hydrocarbon alpha-amino acids. especially those acids having relatively short chain carbon skeletons. Thus. by controlline the amount or DL-methionine units and the o! the extracan be prepared with a wide lanes or properties. Thisvaried raneeoi roperfleseasily aflordsthe preparation from the same intermediates 0! al ha-amino acid many or the properties useful in general mm and fiber outlets to any desired degree.

The i'oregoing detailed description has been given for clearness or understandins only and no are to be modifications will occur to those skilled in the art.

What is claimed is: 1. DL-methionine-N-carboanhydride. 2. A linear polyamide. the chain of which consists or recurring atom groups and the recurring units of which are DL-methionine units.

ROBERT N. MACDONALD.

References Cited in the file 0! this patent UNITED STATES PATENTS Number Name Date 2.534.283 MacDonald Dec. 19, 1950 2,572,844 MacDonald Oct. 30. 1951 OTHER-REFERENCES vol. 173, 

1. A COPOLYMER OF (A) A POLYMERIZATION ESTER OF A POLYBASIC ACID WHICH IS FREE FROM ALIPHATIC UNSATURATION AND AN UNSATURATED MONOHYDRIC ALCOHOL WHICH CONTAINS 3 TO 10 CARBON ATOMS AND AN ALIPHATIC POLYMERIZABLE UNSATURATED CARBON TO CARBON LINKAGE BETWEEN THE BETA AND GAMMA CARBON ATOMS AND (B) A MALEIMIDE WHICH HAS THE GENERAL STRUCTURE 